Choke valve

ABSTRACT

A valve ( 2 ) has a body ( 4 ) defining a flow inlet ( 6 ), a flow outlet ( 8 ) and a valve chamber ( 10 ). A compression coil spring ( 24 ) is contained within the chamber ( 10 ) and its coils ( 32 ) divide the inlet ( 6 ) from the outlet ( 8 ). One end of the spring ( 24 ) is seated against a reaction block ( 20 ) and an actuating rod ( 16 ) extending into the valve chamber ( 10 ) bears on the block enabling it to be lowered or raised. This action causes the size of the helical gaps ( 34 ) between the coils ( 32 ) of the spring to be altered which adjusts the flow of fluid through the valve.

The present invention relates to choke valves used for the control ofpressure and/or flow rates in systems such as hydrocarbon productionsystems.

Typically, in hydrocarbon production systems in which a number ofseparate flows at different pressures feed into a common manifold, achoke valve is incorporated in each flow to optimise the total flow atsome common pressure. Some choke valves are configured with a fixedorifice area and can only be changed by substituting a different sizedorifice. Other choke valves are arranged with adjustable orifices. Acommon configuration is for the flow to be arranged to pass from aninlet port of the choke valve into an annular chamber, so that equalpressure is available at diametrically opposed circular orifices locatedin an inner wall of the chamber. A plain cylindrical annular controlsleeve is arranged to uncover these orifices to a greater or lesserextent thereby providing the control parameter. Pressure is dissipatedwithin a central chamber of the valve by allowing these diametricallyopposite flows to impinge upon each other thereby absorbing energy. Themore the fluid flows collide, the more energy is absorbed. Aftercollision, the fluid flows turn through 90° and are discharged from thevalve.

A disadvantage of this arrangement is that for the linear distance movedby the control sleeve, a variable orifice area is uncovered or covered,which gives a non-linear change in the control parameter. Anotherdisadvantageous feature, is that at very small orifice openings, andwith a high pressure drop across the orifices, very high erosion wearresults from the high velocity jets of production fluids generated underthese conditions. This concentrated wear takes the form of grooves wornin walls defining the orifices and in end regions of the control sleevewhich move over the orifices. This phenomenon is commonly referred to aswire drawing. When the fluid contains abrasive particles, e.g. sand,erosion will occur particularly rapidly. When operating in the nearlyclosed part of the valve envelope, this erosion wear changes thecharacteristics of the valve such that early replacement is necessary,and/or costly trim components for the valve are required to extend itslife. Furthermore, the end region of the sleeve, which moves over theorifices, may be designed to seal against an annular valve seat when thevalve is fully closed. Such sealing may become impossible when theerosion described above has occurred and the valve may lose itsisolating capability.

The object of the invention is to overcome at least some of theabove-mentioned problems of the prior art adjustable choke valves.

Thus, according to the invention, there is provided a valve comprising achoke means defining at least one passageway and control means foradjusting the size of the at least one passageway to adjustably choke aflow of fluid through the valve wherein the choke means includes springmeans with parts between which the at least one passageway is situatedwhereby deformation of the spring means by the control means alter thesize of the at least one passageway for adjusting the flow of fluidthrough the valve.

By providing the passageways between parts of a spring means, localisederosion as discussed above can be avoided since at least one passagewaycan be configured to comprise one or more extended passageways whichspread out the areas of the valve components exposed to wear and therebyavoids localised erosion. A more linear relationship between volumetricflow rate through the valve and movement of the control means can alsobe achieved.

In order to slow the fluid passing through the valve and absorb itsenergy, preferably the spring means is configured such that at least onepassageway includes confronting parts which act to direct parts of thefluid flow against each other to dissipate flow energy.

Conveniently the spring means is substantially cylindrical and the flowof fluid passes between a region inside and a region outside the springmeans as it passes through the valve.

So as to reduce the chance of the valve being clogged as it approachesits fully closed state and when used with fluid containing particles,preferably the spring means has different stiffnesses at differentpoints along its length such that choking of the fluid flow through theat least one passageway occurs at different rates along its length asthe control means is adjusted. With such an arrangement, if for examplethe spring means comprises an array of passageways between individualspring elements, then the stiffness of the elements can be graded or atleast be different so that closure of the passageways occursprogressively as the valve is closed. In this way, immediately prior tocomplete closure, one relatively large passageway can remain open asopposed to a plurality of relatively smaller ones. This largerpassageway will permit larger particles to pass through the valvewithout becoming lodged therein.

In order to minimise the number of components in the valve and when flowvelocities are not likely to cause unwanted resonant vibrations orharmonics in the spring means, it may comprise a coil spring, the atleast one passageway being defined between coils thereof and the controlmeans being arranged to vary an axial length thereof. With such anarrangement, the passageway may comprise a single helical passagewaydefined between the coils of the spring.

So as to enable the valve to dissipate more energy from fluid flowingthrough the valve, the spring means may comprise plural coil springssubstantially concentrically disposed in order that fluid passingthrough the spring means successively passes through two or more sets ofcoils.

When the flow through the valve is sufficiently high that resonantvibration of the spring means is likely to be a problem and/or if thereis a requirement for the stiffness to be different in different parts ofthe spring means, the spring means preferably comprises a plurality ofdiscrete spring elements arranged to bear directly or indirectly on eachother.

Preferably at least some of the spring elements each include pluralapertures through which the fluid flows in order to dissipate energyfrom fluid flowing through the valve. More preferably, at least some ofthe apertures of adjacent spring elements substantially confront eachother so that fluid flows passing through such confronting aperturesimpinge on each other to dissipate still more flow energy.

Conveniently the spring elements are spring washers such as Belvillewashers.

In order to hold the spring elements in place relative to each other andfurther components of the valve, the spring means preferably includesannular locating rings interposed between adjacent spring washers.

In order to increase the amount of energy dissipated by fluid flowingthrough the valve, preferably adjacent locating rings includecomplementary confronting surfaces which define one of said at least onepassageway.

The locating means may be configured to direct or otherwise control theflow path of fluid passing through the valve. For example, the springwashers may be disposed in an axial array with a central longitudinalaxis and the confronting surfaces of the locating rings may be disposedat an oblique angle to the longitudinal axis. The oblique angle may bebetween 20° and 70° and the flow may be directed away from the directionin which the flow passes when leaving the valve.

One or both of the radially inner or outer peripheries of the springwashers may have a set of locating rings interposed therebetweenincluding said complementary surfaces. When two sets of locating ringsare provided, both including said complementary surfaces, a high levelof flow energy dissipation will be achieved.

When less energy dissipation is required, the locating rings between oneof the inner or outer peripheries of the spring washers may merely actto hold the spring washers in position relative to each other. In orderto increase the range of applications in which the valve can be used,preferably full compression of the spring means by the control meansacts to at least substantially close the at least one passageway tothereby at least substantially prevent flow through the valve.

The invention will now be described by way of example only withreference to the accompanying schematic drawings in which:

FIG. 1 is a cross-section of a first embodiment of the invention;

FIG. 2 is a cross-section of a second embodiment of the invention in anopened state;

FIG. 2A is an enlarged view of the area marked A in FIG. 2;

FIG. 3 is a cross-section of the second embodiment of the invention in aclosed state;

FIG. 4 is a cross-sectional detail showing an interface between twoadjacent locating rings of the second embodiment;

FIG. 5 shows a series of views of two confronting surfaces of thelocating rings of FIG. 4 as they move relative to each other;

FIG. 6 is a cross-sectional detail showing an alternative interfacebetween the locating rings of the second embodiment;

FIG. 7 shows a series of views of two confronting surfaces of thelocating rings of FIG. 6 as they move relative to each other;

FIG. 8 is a cross-section of a third embodiment of the invention in anopen state; and

FIG. 9 is a cross-section of the third embodiment in a closed state.

FIG. 1 shows a valve 2 constituting the first embodiment of theinvention which includes a body 4 defining an inlet 6, an outlet 8 and avalve chamber 10. A cover 12 closes an upper end of the chamber 10 andhas a through bore 14 which slidably receives an actuating rod 16 with ahead 18 on its lower end. The head 18 bears on the upper end of areaction block 20, the lower end of which has a downwardly projectingannular rim 22 against which one end of a compression coil spring 24 isseated. The coil spring 24 is formed from a helically configured memberof circular cross section. The lower end of the coil spring 24 is seatedaround an annular rim 26 of the valve body 4 which projects into thevalve chamber 10 away from the outlet 8. An exterior region 28 of thevalve chamber 10 and the inlet 6 are divided from an interior region 30of the valve chamber 10 and the outlet 8 by the coils 32 of the coilspring 24 when the head 18 has been fully lowered by the actuating rod16 so that circumferential surfaces of individual coils 32 of the spring24 are forced into contact with each other. For complete closure of thevalve, it is necessary for the ends of the spring to seal against therims 22 and 26.

The valve is opened by raising the reaction block 20 by means of theactuating rod 16 so that the spring 24 is progressively released and ahelical gap or passageway 34 opens up between the coils 32 of thespring. Fluid entering the valve through the inlet 6 can then pass fromthe exterior region 28 to the interior region 30 of the valve chamber 10by passing inwardly through the gap 34 between the coils of the spring24 as shown at B and C. Flow energy of the fluid is dissipated as thisoccurs.

Due to the fact that flow into the interior region 30 is allsubstantially radially inwardly directed, substantially confrontingportions of the gap 34 will provide flows which will impinge againsteach other (as indicated by arrows B and C) thus dissipating energy.Fluid in the interior region 30 can leave the valve via the outlet 8.

Spring erosion resulting from fluid, possibly containing abrasiveparticles, passing through the gap 34, occurs evenly along the length ofthe gap 34 and localised high erosion rates are avoided. Furthermore,the relationship between the flow rate and displacement of controlmeans, in the form of the actuating rod 16, will be much closer to alinear relationship than for the conventional type of valve referred toabove.

The parts which act to control flow through the valve are convenientlyformed as one element and the sliding of surfaces of such parts againsteach other can be avoided. The relatively long length and relativelyshort width of the gap 34 assists in dissipating flow energy and thelength of the gap 34 can be easily altered by employing a spring havingmore or less coils. The cross-sectional shape of the wire of the springcan be varied to optimise flow conditions. The velocity gradient of theflow is less steep than for a sharp-edged orifice which leads to lessturbulence and quieter operation for a given flow rate.

A cascaded flow path can be provided by utilising plural springs nestedwithin one another, possibly with the helixes of circumferentiallyadjacent springs being disposed in opposite directions.

Although a compression spring is referred to a similar effect could beachieved with a tension spring.

The second embodiment of the invention is shown in FIG. 2. The valve 40includes a body 42 with an inlet 44, an outlet 46 and a valve chamber 48closed by a cover 50 having a through bore 52 which slidingly receivesan actuating rod 54 which projects into the chamber 48 where it isconnected to a reaction block 56.

Concentrically disposed with respect to a central axis 62 of the outlet46 is a stack 64 of spring washers 66 (such as Belville washers) whichtend to spring back to a non-flat configuration as shown in FIG. 2 whenflattened. As shown in FIG. 2A, which is an enlarged detail of region Aof FIG. 2, the stack 64 comprises pairs 68 of spring washers 66 withtheir adjacent outer peripheries 70 located in annular recesses 72 ofannular outer locating rings 73.

The inner peripheries 74 of adjacent spring washers 66 of adjacent pairs68 thereof, as shown in detail in FIG. 4, are located in externallyfacing annular recesses 76 in annular inner locating rings 78. FIG. 5shows a series of cross-sectional views of adjacent parts of two ofthese inner locating rings 78 as they move into contact with each otherand separate. Confronting surfaces 80 of the locating ring 78 aredisposed at an angle α to the direction of the central axis 62. In theinner locating rings 78 shown in FIGS. 4 and 5, this angle α is 60°.

The uppermost and lowermost spring washers of the stack 64 (as viewed inFIG. 3) have their inner peripheries engaged in a recess in modifiedlocating rings. The uppermost locating ring 82 is sealed in a recess 86in a lower surface of the reaction block 56 and the lowermost locatingring 84 is sealed in a recess 88 in the body 42 of the outlet 46.

Each spring washer 66 has plural perforations 90 (two per washer shownin FIG. 2), between its inner 74 and outer 70 peripheries. Theperforations 90 of each pair 68 of spring washers are aligned with eachother.

When the reaction block 56 is lowered so as to fully compress the stack64 of spring washers 66, as shown in FIG. 3, the confronting surfaces 80of the inner locating rings 78 are forced into sealing contact with eachother and flow between exterior 58 and interior 60 regions of the valvechamber situated respectively outside and inside the stack 64, isprevented.

As downward force on the actuating rod 54 is released, the reactionblock 56 is forced upwardly by resilience of the stack of spring washers66 and passageways 92 open up between the confronting surfaces 80 of thelocating rings 78. This permits fluid to enter the inlet 44 and passthrough the perforations 90. Each flow through a perforation 90 willcollide with a complementary flow through a confronting perforation 90,as shown at D in FIG. 2A. The flows will then pass through thepassageways 92 and be directed at the angle α to the central axis 62inwardly and upwardly towards a concave lower surface 94 of the reactionblock 56. Flows from diametrically opposed portions of each passageway92 will collide with each other as shown at. E, thereby dissipating.further energy and the flows will then be diverted towards the outlet 46and leave the valve.

Depending on the flow velocities, dimensions, energy absorbingrequirements etc. the angle α may be other than 60° and could forexample be 30° as shown in FIGS. 6 and 7 in which parts which correspondto those shown in FIGS. 4 and 5 are designated with like numerals andare accordingly not described. below.

In order to provide progressive opening and closing of the passageways92, the spring washers 66 may have graded stiffnesses. For example, ifthe stiffness of the spring washers 66 increases towards the bottom ofthe stack, then the lowermost passageway 96 will be the first to openand the uppermost passageway will be the last to open. Conversely, thelowermost passageway will be the last to close. Accordingly, immediatelyprior to complete closure of the valve, a single relatively widepassageway 96 will remain open. In contrast, if all spring washers havethe same stiffness then plural relatively narrow passageways will beleft open leading to a higher chance of particles becoming trappedtherein. Other stiffness variations are possible. Stiffer washers couldbe located at the middle of the stack 64 or a single stiffer springwasher or pair of spring washers could be included.

FIGS. 8 and 9 show a third embodiment of the invention. Parts whichcorrespond to those shown in FIGS. 2-5 are designated by the samenumerals and are not described below.

The valve 102 shown in FIGS. 8 and 9 differs from that shown in FIGS. 1and 2 in that its outer locating rings 104 are configured similarly tothe inner locating rings 78 of the FIG. 2 embodiment in that theyinclude confronting surfaces which seal against, or at least come closeto each other, when the reaction block is fully lowered so that theinner locating rings 78 seal against each other. As a consequence,further dissipation of flow energy will occur as the flow passesinwardly through the passageways 106 between the outer locating rings104.

The uppermost and lowermost spring washers (i.e. those at opposite endsof the stack 64) do not contain perforations 90. This is so that allfluid entering the interior region 60 of the stack 64 is constrained topass through a throttling passageway between two adjacent outer locatingrings in addition to passing through a throttling passageway 92 betweenthe-adjacent inner locating rings.

FIG. 8 shows the valve 102 in its open state with the stack 64uncompressed, and FIG. 9 shows the valve 102 in its closed state withthe stack 64 completely compressed.

The spring washers 66 in the embodiment shown in FIG. 8 may havedifferent stiffnesses, passageway orientations etc. as described abovewith reference to the FIG. 2 embodiment.

As with the coil spring embodiment of FIG. 2, the overall maximumpassageway area can be easily modified by employing more or less springwashers.

Since the locating rings are easily manufactured discrete annular parts,they can be manufactured with properties suiting particular erosion,cavitation, sealing etc. requirements independent of the properties ofthe spring washers.

1. A valve (40) comprising a choke means defining at least onepassageway (92) and control means (54, 56) for adjusting the size of theat least one passageway to adjustably choke a flow of fluid through thevalve wherein the choke means includes spring means (64) with partsbetween which the at least one passageway is situated wherebydeformation of the spring means (64) by the control means alter the sizeof the at least one passageway for adjusting the flow of fluid throughthe valve, characterized in that the spring means comprises a pluralityof discrete spring elements (66) arranged to bear directly or indirectlyon each other.
 2. The valve as claimed in claim 1, wherein the springmeans (64) is configured such that the at least one passageway (92)includes confronting parts which act to direct parts of the fluid flowagainst each other to dissipate flow energy.
 3. The valve as claimed inclaim 1, wherein the spring means (64) is substantially cylindrical andthe flow of fluid passes between a region (58) outside and a region (60)inside the spring means as it passes through the valve (40).
 4. Thevalve as claimed in claim 1, wherein the spring means (64) has differentstiffnesses at different points along its length such that choking ofthe fluid flow through the at least one passageway occurs at differentrates along its length as the control means (54, 56) is adjusted.
 5. Thevalve as claimed in claim 1, wherein at least some of the springelements (66) each include plural apertures (90) though which the fluidflows.
 6. The valve as claimed in claim 5, wherein at least some of theapertures (90) of adjacent spring elements (66) substantially confronteach other.
 7. The valve as claimed in claim 1, wherein the springelements comprise spring washers (66).
 8. The valve as claimed in claim7, wherein the spring means (64) includes annular locating rings (78)interposed between adjacent spring washers (66).
 9. The valve as claimedin claim 8, wherein the adjacent locating rings (78) includecomplementary confronting surfaces (80) which define one of said atleast one passageway.
 10. The valve as claimed in claim 9, wherein thespring washers (66) are disposed in an axial array with a centrallongitudinal axis (62) and the confronting surfaces (80) of the locatingrings (78) are disposed at an oblique angle to the longitudinal axis.11. The valve as claimed in claim 10, wherein the oblique angle isbetween 20° and 70°.
 12. The valve as claimed in claim 10, wherein thespring washers which are at opposite ends of the axial array are free ofapertures.
 13. The valve as claimed in claim 9, wherein radially inneror outer peripheries of the spring washers (66) have a first set oflocating rings (78) interposed therebetween including said complementaryconfronting surfaces (80).
 14. The valve as claimed in claim 13, whereinthe other of the radially inner or outer peripheries of the springwashers (66) have a second set of locating rings (104) interposedtherebetween including said complementary confronting surfaces.
 15. Thevalve as claimed in claim 13, wherein the other of the radially inner orouter peripheries of the spring washers have locating rings (73)therebetween which merely act to hold the spring washers in positionrelative to each other.
 16. The valve as claimed in claim 1, whereinfull compression of the springs means (64) by the control means (54, 56)acts to at least substantially close the at least one passageway (92) tothereby at least substantially prevent flow through the valve (40). 17.(canceled)
 18. (canceled)
 19. (canceled)